If there is a "Revolution Plan (WIP)" document shared amongst a few agitators, and someone in power gets their hand on it (and its "checksum" or whatever), then can they figure out _who else_ has it?
More or less, yes. Apple could search for a list of iCloud users with that hash in their account and single them out without breaking the encryption (not that they can't do that too).
If there is a "Revolution Plan (WIP)" document shared amongst a few agitators, and someone in power gets their hand on it (and its "checksum" or whatever), then can they figure out _who else_ has it?